Chapter 6 Computer Networking The Link Layer A TOP-DOWN APPROA⊙升TH0T米 and LANs KUROSE·ROSS A note on the use of these Powerpoint slides: We're making these slides freely available to all (faculty,students,readers). Theyre in PowerPoint form so you see the animations:and can add,modify. and delete slides (including this one)and slide content to sut your needs. They obviously represent a lot of work on our part.In return for use,we only ask the following: Computer If you use these slides (e.g..in a class)that you mention their source Networking:A Top (after all,we'd like people to use our book!) If you post any slides on a www site.that you note that they are adapted from (or perhaps identical to)our slides,and note our copyright of this Down Approach material. 7th edition Thanks and enjoy!JFK/KWR Jim Kurose,Keith Ross noReered Pearson/Addison Wesley April 2016 Link Layer and LANs 6-1
Computer Networking: A Top Down Approach A note on the use of these Powerpoint slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: ▪ If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!) ▪ If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR All material copyright 1996-2016 J.F Kurose and K.W. Ross, All Rights Reserved 7 th edition Jim Kurose, Keith Ross Pearson/Addison Wesley April 2016 Chapter 6 The Link Layer and LANs Link Layer and LANs 6-1
Chapter 6:Link layer and LANs our goals: understand principles behind link layer services: error detection,correction sharing a broadcast channel:multiple access link layer addressing local area networks:Ethernet,VLANs instantiation,implementation of various link layer technologies Link Layer and LANs 6-2
Chapter 6: Link layer and LANs our goals: ▪ understand principles behind link layer services: • error detection, correction • sharing a broadcast channel: multiple access • link layer addressing • local area networks: Ethernet, VLANs ▪ instantiation, implementation of various link layer technologies Link Layer and LANs 6-2
Link layer,LANs:outline 6.I introduction,services 6.5 link virtualization: 6.2 error detection, MPLS correction 6.6 data center 6.3 multiple access networking protocols 6.7 a day in the life of a 6.4 LANs web request ·addressing,ARP ·Ethernet ·switches ·VLANS Link Layer and LANs 6-3
Link layer, LANs: outline 6.1 introduction, services 6.2 error detection, correction 6.3 multiple access protocols 6.4 LANs • addressing, ARP • Ethernet • switches • VLANS 6.5 link virtualization: MPLS 6.6 data center networking 6.7 a day in the life of a web request Link Layer and LANs 6-3
Link layer:introduction terminology: hosts and routers:nodes communication channels that connect adjacent nodes along communication path:links 。wired links ·wireless links ·LANs layer-2 packet:frame, encapsulates datagram data-link layer has responsibility of transferring datagram from one node to physically adjacent node over a link Link Layer and LANs 6-4
Link layer: introduction terminology: ▪ hosts and routers: nodes ▪ communication channels that connect adjacent nodes along communication path: links • wired links • wireless links • LANs ▪ layer-2 packet: frame, encapsulates datagram data-link layer has responsibility of transferring datagram from one node to physically adjacent node over a link Link Layer and LANs 6-4
Link layer:context datagram transferred by transportation analogy: different link protocols over trip from Princeton to Lausanne different links: limo:Princeton to JFK e.g.,Ethernet on first link, ·plane:JFK to Geneva frame relay on train:Geneva to Lausanne intermediate links,802.II ■tourist=datagram on last link transport segment each link protocol provides communication link different services ■ transportation mode link 。eg,may or may not layer protocol provide rdt over link travel agent routing algorithm Link Layer and LANs 6-5
Link layer: context ▪ datagram transferred by different link protocols over different links: • e.g., Ethernet on first link, frame relay on intermediate links, 802.11 on last link ▪ each link protocol provides different services • e.g., may or may not provide rdt over link transportation analogy: ▪ trip from Princeton to Lausanne • limo: Princeton to JFK • plane: JFK to Geneva • train: Geneva to Lausanne ▪ tourist = datagram ▪ transport segment = communication link ▪ transportation mode = link layer protocol ▪ travel agent = routing algorithm Link Layer and LANs 6-5
Link layer services framing,link access: encapsulate datagram into frame,adding header,trailer channel access if shared medium ·“MAC”addresses used in frame headers to identify source,destination different from IP address! reliable delivery between adjacent nodes we learned how to do this already (chapter 3)! seldom used on low bit-error link(fiber,some twisted pair) wireless links:high error rates Q:why both link-level and end-end reliability? Link Layer and LANs 6-6
Link layer services ▪ framing, link access: • encapsulate datagram into frame, adding header, trailer • channel access if shared medium • “MAC” addresses used in frame headers to identify source, destination • different from IP address! ▪ reliable delivery between adjacent nodes • we learned how to do this already (chapter 3)! • seldom used on low bit-error link (fiber, some twisted pair) • wireless links: high error rates • Q: why both link-level and end-end reliability? Link Layer and LANs 6-6
Link layer services(more) ■flow control: pacing between adjacent sending and receiving nodes error detection: errors caused by signal attenuation,noise. receiver detects presence of errors: signals sender for retransmission or drops frame error correction: receiver identifies and corrects bit error(s)without resorting to retransmission half-duplex and full-duplex with half duplex,nodes at both ends of link can transmit,but not at same time Link Layer and LANs 6-7
▪ flow control: • pacing between adjacent sending and receiving nodes ▪ error detection: • errors caused by signal attenuation, noise. • receiver detects presence of errors: • signals sender for retransmission or drops frame ▪ error correction: • receiver identifies and corrects bit error(s) without resorting to retransmission ▪ half-duplex and full-duplex • with half duplex, nodes at both ends of link can transmit, but not at same time Link layer services (more) Link Layer and LANs 6-7
Where is the link layer implemented? ■in each and every host link layer implemented in “adaptor”(aka network interface card NIC)or on a chip application Ethernet card,802.1I transport network cpu memory card;Ethernet chipset link implements link,physical host layer bus (e.g.,PCI) attaches into host's system link physical buses physical trans ssion combination of hardware, software,firmware network adapter card Link Layer and LANs 6-8
Where is the link layer implemented? ▪ in each and every host ▪ link layer implemented in “adaptor” (aka network interface card NIC) or on a chip • Ethernet card, 802.11 card; Ethernet chipset • implements link, physical layer ▪ attaches into host’s system buses ▪ combination of hardware, software, firmware controller physical transmission cpu memory host bus (e.g., PCI) network adapter card application transport network link link physical Link Layer and LANs 6-8
Adaptors communicating datagram datagram controlle sending host receiving host datagram frame sending side: receiving side encapsulates datagram in looks for errors,rdt, frame flow control,etc. adds error checking bits, extracts datagram,passes rdt,flow control,etc. to upper layer at receiving side Link Layer and LANs 6-9
Adaptors communicating ▪ sending side: • encapsulates datagram in frame • adds error checking bits, rdt, flow control, etc. ▪ receiving side • looks for errors, rdt, flow control, etc. • extracts datagram, passes to upper layer at receiving side controller controller sending host receiving host datagram datagram datagram frame Link Layer and LANs 6-9
Link layer,LANs:outline 6.I introduction,services 6.5 link virtualization: 6.2 error detection, MPLS correction 6.6 data center 6.3 multiple access networking protocols 6.7 a day in the life of a 6.4 LANs web request ·addressing,ARP ·Ethernet ·switches ·VLANS Link Layer and LANs 6-10
Link layer, LANs: outline 6.1 introduction, services 6.2 error detection, correction 6.3 multiple access protocols 6.4 LANs • addressing, ARP • Ethernet • switches • VLANS 6.5 link virtualization: MPLS 6.6 data center networking 6.7 a day in the life of a web request Link Layer and LANs 6-10
